The corners. A double rail configuration puts twice the timber where the beams meet the posts, and heavy-duty corner bracing locks that joint. The result is a frame that flexes less under load and in wind, which matters if you are adding a roof kit, sitting the pergola over a hot tub or building in an exposed garden. Everything else, from the redwood to the decking base, matches the standard model.

Five square sizes: 2.4m by 2.4m, 3m by 3m, 3.6m by 3.6m, 4.2m by 4.2m and 4.8m by 4.8m, each in Rustic Brown or Light Green. Prices start from £978.99 and depend on the size, the finish and the roof and screening options you pick. Bespoke footprints are made to order if your garden does not suit one of the five standard sizes.

The double rail corners and bracing are the reason people choose this model for a hot tub. The pergola frames and shelters the tub rather than carrying it, so the tub sits on its own supporting base as the manufacturer specifies. Add a polycarbonate roof kit if you want to use it in the rain, and fix the pergola down at the same time so the roof has something solid holding it.

Straightforward for two people with a drill and a level. The precision notched design means the rails and rafters drop into cut seats rather than being measured and positioned by eye, which removes most of the guesswork. Lay the decking base first on firm, reasonably level ground, then work up through posts, rails, bracing and rafters. Allow the better part of a day on the larger sizes.

Yes, though not often. The pressure treatment inside the wood handles rot and fungal decay, but the Rustic Brown or Light Green finish on the surface weathers, so plan on re-coating with a suitable exterior timber stain every two to three years. Pick a dry spell so the stain soaks in, and keep leaves and soil away from the foot of each post between times.